1. Field of the Invention
The invention concerns a transporter for installation or removal of an offshore platform comprising a jacket and a topsides supported by the jacket, the topsides comprising one ore more decks. The invention also concerns a method for removal of an offshore platform comprising a jacket and a topsides supported by the jacket.
2. Description of the Prior Art
The installation of offshore platforms is relevant in connection with the development of oil and gas fields at sea.
The removal of offshore platforms, consisting of a jacket and a topsides supported by the jacket, is a field which will become more important in the coming years, with the decommissioning of a number of offshore platforms.
Offshore platforms can be removed by being split up into smaller parts, for example by means of cutting torches or blasting, whereupon each of these smaller parts can be lifted aboard a barge or a ship and transported away. Regardless of how the splitting up is carried out, however, the costs associated with the breaking up and subsequent transport in smaller parts are substantial.
Thus it is a wish to split up a platform which has to be removed into the fewest possible parts, in which case a natural division is to divide it into topsides and jacket, each of which is removed separately. In the case of small platforms with low weight this is relatively problem-free, while in the case of large and heavy platforms it entails lifting with extremely large and expensive crane vessels, if it is even possible at all within the scope of what can be implemented in practice.
The applicant""s Norwegian patent applications Nos. 973561, 973562 and 973563 respectively disclose a method and a transporter for installation or removal of a jacket for an offshore platform, a method and a transporter for installation or removal of an offshore platform topsides and a transporter for heavy objects at sea. However, these applications are only describing relevant methods and equipment for handling parts of offshore platforms, such as topsides or jackets. In Norwegian patent application No. 965439 (abandoned before published) there has been decribed a device for such use, comprising a main unit formed by a barge-like structure with adjustable buoyancy, which can be transported, lowered, manouvered and raised in water, characterized in that an auxiliary unit adapted to cooperation with the main unit comprises means for releasable connection to the main unit in at least two different ways, and means for controlling the main unit""s functions. This embodiment is not a part of the priority claimed from the above-mentioned Norwegian patent applications Nos. 973561, 973562 and 973563.
Norwegian patent applications No. 973561, 973562 and 973563 disclose methods and transporters which together enable removal of an offshore platform in a favourable way, by splitting the platform in jacket and topsides only and remove these two parts separately. The same methods and transporters may also be used for installation of an offshore platform.
The object of the invention is to provide a transporter for removal or installation of an offshore platform comprising a jacket and a topsides supported by the jacket, the topsides comprising one ore more decks, which transporter shall be able to carry the jacket and the topsides simultaneously. The object is further to provide a method for removal of an offshore platform comprising a jacket and a topsides supported by the jacket, using the transporter according to the invention, in which method the removal of the topsides shall be followed by the successive removal of the jacket without any need for an intermediate transfer of the topsides to a receiver.
The invention is thus an improvement in relation to Norwegian patent applications Nos. 973561, 973562 and 973563, using the same construction elements in combination. The invention thus consist of a combined transporter comprising features that enables manipulation of both the topsides and the jacket, and carrying out these simultaneously. The invention enables removal of an offshore platform without the use of cranes. The invention also enables simultaneous movement of the topsides and the jacket to a receiver, e.g. a construction yard or a quay, using only one and the same transporter.
Provided a rotation of the topsides is acceptable prior to installation, a method corresponding to the method according to the invention may be used for installation of an offshore platform, with the steps performed in the reverse order. This is a clear variant of the method according to the invention, and will not be explained in detail. It should be understood, however. that the inventive concept also covers this alternative.
Further scope of the applicability of the present invention will become apparent from the, detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.